1. Field of the Invention
This invention relates to spacecraft attitude and/or orbit control systems and is particularly directed to systems for controlling spacecraft nutation caused by external forces and torques used to change spacecraft attitude or orbit.
2. Description of the Prior Art
A problem frequently encountered in applying thrust forces from thrusters in dual-spin or spin stabilized spacecraft for controlling spacecraft attitude and/or station keeping orbital adjustments is an undesirable spacecraft nutation or coning movement. Spacecraft nutation is caused by a misaligned torque due to a thrust force directed along an axis which does not pass through the spacecraft center of gravity. Such a thrust force will be referred to as a misaligned thrust force. The nutation causing torque resulting from the misaligned thrust force has a component at right angles to the spacecraft's total momentum vector. Many systems have been proposed heretofore for controlling such undesirable spacecraft nutation. Some prior art attitude and/or orbit control systems use a combination of passive elements arranged to dissipate the undesirable spacecraft nutation. Other prior art attitude and/or orbit control systems counteract spacecraft nutation by use of an external force or forces generated by special spacecraft thrusters activated by electrical signals from sensors which detect spacecraft nutation.
A combination of special nutation counteracting thrusters and sensors or passive elements arranged solely for the dissipation or damping of spacecraft nutation due to thrust force misalignment increase the complexity of spacecraft control system design. Accordingly, it is desirable to minimize spacecraft nutation caused by thrust misalignments without substantially increasing the complexity of spacecraft attitude and orbit control systems.